1. Field of the Invention
The present invention relates to new perfluoroalkanes and haloperfluoroalkanes, characterized by having a low melting point and high thermal and chemical stability, constituted by preferably branched perfluorinated or haloperfluorinated chains.
More particularly, the invention relates to new preferably branched perfluoroalkanes and haloperfluoroalkanes, obtained from percursors characterized by containing in their chain two halogen atoms equal to or different from each other, one of which necessarily being a iodine atom.
A further purpose of the present invention is to provide a process for the synthesis of said preferably branched perfluoroalkanes or haloperfluoroalkanes, by a method which can be easily implemented on an industrial scale.
2. Description of the Prior Art
Perfluoroalkanes are known which are obtained by means of the Phillips electrochemical fluorination process (U.S. Pats. Nos. 3,511,760 and 3,511,761), which can be suitably used for the synthesis of several compounds, among which perfluoroalkanes too. The limitation of this process derives both from the fact that it results expensive as regards the equipment installation and, above all, the energetic viewpoint, and from the fact that it allows conveniently fluorinating only compounds having a low molecular weight. pounds (products of up to six carbon atoms).
Also perfluoroalkanes obtained by anionic aligomerization of perfluoroolefins (U.S. Pat. Nos. 3,917,724 and 3,962,358) and subsequent fluorination of the double bonds are known, but the useful products which can be obtained are perfluoroalkanes of either 6 or 9 carbon atoms, whilst the other oligomers obtainable in practice show a high branching degree, which reduces the stability of such products (see J. Fluor. Chem. (1981) 18 417).
Perfluoroalkanes are furthermore known, which are obtained by starting from aromatic hydrocarbons, such as, e.g., toluene, by fluorination with CoF.sub.3, but this synthesis requires the use of particularly sophisticated equipment, withstanding both the fluorine used to regenerate the CoF.sub.3 which is reduced during the synthesis, and the high temperatures normally required for their synthesis. Moreover, as the reaction proceeds, the replacement of the hydrogen atoms of the hydrocarbon used as the precursor of the perfluorinated compounds to be prepared, becomes more and more difficult, so that a not completely fluorinated fluid is obtained, containing byproducts still having hydrogen atoms.
The presence of these byproducts decreases, among others, the thermal stability, the thermal and chemical inertia of the product, thus limiting the application field of these fluorinated fluids.
Moreover, the methods for the separation of said not completely fluorinated byproducts are very expensive and difficult to be carried out.
Iodoperfluoroalkanes can be obtained by telomerizing tetrafluoroethylene with such telogens as CF.sub.3 I, C.sub.2 F.sub.5 I, C.sub.3 F.sub.7 I.
In this case, their preparation results anyway difficult, as CF.sub.3 I can be obtained ony by the decomposition of CF.sub.3 COOAg in the presence of iodine (Hunsdiecker reaction), and for the other two products the use of IF is required, which is notoriously difficult to be synthetized and handled.